1. Field of the Invention
The present intervention relates to an improved system for sterilizing articles utilizing ultraviolet radiation.
2. Description of the Prior Art
At present, food packaging products such as dairy product cartons, lids, sealing films, plastic wrap, labels, reusable product containers and other articles used in the packaging of products are sanitized by ultraviolet irradiation. In conventional food packaging and container sanitizing operations the articles to be treated are passed on a conveyor beneath a conventional lamp that emits ultraviolet radiation. The ultraviolet lamp is driven by a magnetic ballast. In order to irradiate and thereby thoroughly sanitize articles on the conveyor system the undersides of the articles resting upon the conveying mechanism must be irradiated, as well as the upper sides.
To irradiate the underside of an article, it has been conventional practice to employ a conveyor belt having an open mesh through which a source of ultraviolet illumination shines. Alternatively, the articles to be irradiated may be placed upon a plurality of narrow, laterally separated belts or chains that support the articles to be irradiated from beneath and convey them through the irradiation tunnel. However, even though both of these conventional systems allow significant portions of the underside of articles transported through the irradiation tunnel to be exposed to ultraviolet radiation, the structures of conventional conveyor systems of this type do cast radiation xe2x80x9cshadowsxe2x80x9d on certain portions of the undersides of the articles being treated. As a consequence, these articles cannot be completely sanitizing by ultraviolet radiation using conventional conveyor systems.
A further difficulty in sanitizing articles conveyed past an ultraviolet irradiation source is that the presence of surfaces parallel to the rays of the irradiation source and also indentations and other nooks and crannies in the articles prevents the ultraviolet radiation from striking all of the surfaces of the articles. Consequently, bacteria can linger untreated in areas on the surfaces of the articles that do not receive direct or reflected ultraviolet radiation.
Still another problem that exists in conventional ultraviolet irradiation tunnels is that the lamps emitting the ultraviolet radiation tend to deteriorate rather rapidly, particularly if they are constructed as elongated tubes. Nevertheless, an elongated tubular shape for the ultraviolet irradiation sources is the best shape for irradiating the entire width of the irradiation tunnel.
The problem that arises is that conventional ultraviolet radiation lamp tubes are supported at their ends, but are unsupported between their ends. Any support between the ends of the tubes would interfere with the radiation emitted. As a consequence, with the intense heat that is built up in the generation of ultraviolet radiation, the tubular structure of the ultraviolet radiation lamps softens and tends to sag at the centers of the lamps. When this occurs radiation is irregular and at a reduced intensity. Also, this deformation of the bodies of the tubes causes structural damage, leading to premature failure of the ultraviolet radiation lamps. The longer the tubes, the greater the likelihood of damage in this connection. Some ultraviolet tubes can have a length as great as 10 feet.
To solve this problem it is conventional practice to periodically rotate the elongated ultraviolet radiation tubes one hundred eighty degrees to reduce the distortion to the structure of the lamp tubes caused by sagging at their centers. This maintenance procedure does prolong the life of the lamp, but requires the combined effort of two persons to rotate each lamp. That is, the supports at both ends of the ultraviolet radiation lamp tubes on both sides of the tunnel must be accessible. This is often difficult or inconvenient, since one side of the tunnel may be located close to a wall of a room in which the tunnel is located. In any event, the individuals performing the task must coordinate their efforts and simultaneously remove the ends of the lamp tubes from their supports and rotate the ends of the tubes one hundred eighty degrees. The ends of the tubes must then be replaced in their supports. This maintenance process is therefore rather time-consuming and requires two people.
The present invention provides an improved system for irradiating articles with ultraviolet radiation within an irradiating tunnel that largely solves the foregoing problems. The system of the present intervention greatly reduces or eliminates completely the problem of xe2x80x9cshadowsxe2x80x9d being cast upon portions of the articles as they are conveyed through the tunnel. The system of the invention also provides a construction that allows a single person to rotate an ultraviolet radiation tube one hundred eighty degrees and reseat it in its support. The unique system of the invention greatly improves the degree of sanitation that is achieved using ultraviolet radiation upon articles conveyed past an ultraviolet irradiation source.
The invention involves a system for irradiating generally flat or collapsible objects such as reusable produce shipping boxes and food packaging materials that have various crevices, openings, and other niches in which bacteria can collect, or even just surfaces that are perpendicular to the path of travel of the articles through the tunnel. In conventional systems in which the objects are transported on a conveyor chain, there is always a xe2x80x9cshadowxe2x80x9d cast by the conveyor chain or drive on the undersides of the items being irradiated as the articles are transported through an irradiation tunnel. These shadows prevent the article from being completely irradiated.
According to the improvement of the invention, the drive chains or belt system upon which the objects are supported is divided into segments in which the conveyor chains or belts of each sequential segment are laterally offset from the conveyor chains of the adjacent conveyor segment or segments. Thus, although a conveyor chain or belt of one segment will cast a shadow on the location of the underside of the article to be irradiated, the shadows are cast upon a different part of the article in the next sequential segment. As a consequence, as the object passes through the tunnel, at one point or another the entire undersurface, as well as the upper surface, is irradiated so that there is no sheltered, shadowed region on the underside of the articles being conveyed. To the contrary, all areas of the undersurface of the article are exposed to ultraviolet radiation sometime during the progression of the article along its path of travel.
A further feature of the invention is the use of nonparabolic reflectors, such as elliptical reflectors. In conventional practice the elongated, tubular ultraviolet radiation lamps are located above and beneath a conveyor system. To maximize the ultraviolet radiation directed at the articles being transported by the conveyor system each elongated ultraviolet lamp is provided with a concave reflector located behind the lamp and facing the articles being transported through the irradiation tunnel. The axis of the lamp is located within the arc of curvature of the reflector. It has been accepted practice in conventional practice for the reflectors to be constructed with a parabolic cross section. As a consequence, ultraviolet radiation that is reflected from the conventional parabolic reflectors travels in parallel paths to impinge upon articles passing on a conveyor system therebeneath.
While such a construction does provide for reflection along the shortest path to reach the article, the fact that the reflected radiation travels in parallel rays means that the reflected radiation is always directed at the article perpendicular to its path of travel. Consequently, surfaces of the article that are oriented perpendicular to the path of travel receive little, if any radiation. The same is true of indentations, niches, slots, and undercuts on the article. These regions are sheltered from the impinging radiation by other portions of the article. With conventional parabolic reflectors, the irradiating light is focused in parallel beams onto the articles passing therebeneath or thereabove. This causes certain surfaces on the article normal to the path of travel, as well as crevices and indentations in the articles to pass through the system without receiving direct ultraviolet radiation.
The improved ultraviolet radiation conveyor system of the present invention greatly alleviates this problem by constructing the reflectors with nonparabolic surfaces which may be elliptical, rather than of a parabolic cross section. With an elliptical reflector the irradiating illumination strikes the surfaces of the articles at different angles as the articles move past the irradiating lamps. Consequently, at some point in the progression of each article along its path of travel the various nooks and indentations in the article receive reflected illumination at an angle from one or more of the irradiating lamps.
A further feature of the invention is the mounting system for the ultraviolet lamps. The ultraviolet lamps are shaped generally as elongated tubular structures, and look much like conventional fluorescent light bulbs in conventional overhead room lighting systems. With the intense heat generated by the emission of ultraviolet radiation, the tubular ultraviolet lamps tend to soften and at their centers. Also, the sides of the lamps facing the reflectors are subject to a much higher level of heat than the sides of the lamps facing the articles passing therebeneath. Therefore, it is advantageous to periodically rotate the lamps about their axes to extend their useful life. In conventional systems this requires two workers, one at each end to lift both ends of the lamps in order to rotate them.
With the mounting system of the present system, one end of each lamp is inserted through an opening, preferably circular, that has a diameter slightly larger than the diameter of the lamp. The other end of the lamp is held by an oblong or bar-shaped constraint. To rotate the lamp, the rectangular bar-shaped constraint is merely lifted out of its inverted U-shaped yoke or saddle, rotated about its own axis one hundred eighty degrees, and reinserted back into the inverted U-shaped saddle. The clearance provided by the opening in the support at the opposite end of the lamp allows the lamp to be tilted while that end rotates in its circular opening. Consequently, the lamp can be rotated by a single person standing at one end of the lamp.
In one broad aspect the present invention may be considered to be an ultraviolet light irradiation apparatus comprising an irradiation tunnel, a conveyor system, at least one upper ultraviolet irradiation source, and at least one lower ultraviolet irradiation source. The tunnel is of conventional construction having an entrance and having an exit longitudinally displaced from the entrance. The conveyor system supports articles to be irradiated from beneath and transports them along a longitudinal treatment path from the entrance to the exit of the tunnel.
Unlike conventional conveyor systems, the conveyor system of the invention includes a plurality of different longitudinally sequential segments. The different sequential segments of the conveyor system contact different laterally separated locations on the articles from beneath. In this way all locations on the article are left unobscured from the irradiation source from beneath at some location on the treatment path within the irradiation tunnel between the entrance and exit thereof. The upper ultraviolet irradiation source is located within the irradiation tunnel for irradiating the articles from above as they are transported along the treatment path. The lower ultraviolet irradiation source irradiates the articles from beneath at the plurality of different longitudinally sequential segments of the conveyor system.
Preferably, each of the different conveyor segments is comprised of a plurality of longitudinally extending, endless conveyor loops lying in parallel, longitudinally aligned, vertical planes spaced apart from each other in a direction perpendicular to the treatment path. The planes in which the endless conveyor loops are aligned on at least two of the different sequential conveyor segments are offset from each other in a direction perpendicular to the treatment path. The endless conveyor loops have longitudinally opposing end extremities. Preferably also, the end extremities of the conveyor loops of each of the conveyor segments overlap and are interleaved between the end extremities of the conveyor loops of each longitudinally adjacent conveyor segment.
To insure adequate irradiation coverage across the width and throughout the length of the irradiation tunnel, at least some of the ultraviolet irradiation sources are often constructed as elongated tubes aligned transverse to the longitudinal path of travel. A plurality of the transverse, upper ultraviolet radiation tubes are located within the tunnel at longitudinal intervals from each other. In the preferred arrangement at least one of the transverse, lower ultraviolet radiation tubes is located beneath the treatment path at each of the different longitudinally sequential conveyor segments.
In another broad aspect the invention may be considered to be a method of irradiating articles utilizing a conveyor system that transports the articles and supports them from beneath along a longitudinal treatment path from an entrance to an exit of an irradiation tunnel. At least one upper ultraviolet irradiation source is located above the longitudinal treatment path and at least one lower ultraviolet irradiation source is located beneath the longitudinal treatment path.
The method of the invention involves supporting the articles from beneath and changing the laterally separated points of contact thereon at different longitudinal locations along the tunnel as the articles are transported along the longitudinal treatment path. This process prevents any parts of the articles facing the irradiation sources from being shadowed from radiation throughout the entire length of the longitudinal treatment path. Preferably, the articles are subjected to ultraviolet radiation from beneath at a plurality of different longitudinal locations along the tunnel. The method of the invention preferably further involves reflecting at least some of the ultraviolet light from at least one of the ultraviolet irradiation sources to thereby irradiate the articles with reflected ultraviolet light that impinges upon the articles at angles that vary as the articles are transported past the ultraviolet irradiation source or sources.
In still another aspect the invention may be considered to be an improvement in an ultraviolet irradiation tunnel in which articles to be irradiated are transported along a longitudinal path past an elongated, ultraviolet irradiation source. The improvement of the invention comprises a concave reflector having a nonparabolic cross-sectional arc of curvature. The reflector faces the longitudinal path. The elongated ultraviolet irradiation source is located within the arc of curvature and between the reflector and the longitudinal path. Since the arc of curvature of the reflector is nonparabolic, light emitted from the irradiation source and reflected by the reflector strikes the passing articles to be sanitized by ultraviolet radiation at different angles as the articles move past the reflector. Preferably the arc of curvature of the reflector has an elliptical shape and a plurality of irradiation sources and reflectors are located at longitudinally separated locations both above and below the longitudinal path. As a consequence, reflected radiation reaches crevices, niches, and surfaces perpendicular to the path of travel to a much greater extent than in conventional irradiation tunnels.
In still another aspect, the invention may be considered to be an improvement in an ultraviolet irradiation tunnel in which articles to be irradiated are transported along a longitudinal path past an elongated, horizontally oriented, ultraviolet radiation lamp having opposing ends. A pair of opposing ultraviolet lamp supports are provided for mounting the opposing ends of the elongated lamp relative to the tunnel. According to the improvement of the invention a first of the ultraviolet lamp supports is secured relative to the ultraviolet irradiation tunnel and has an opening therethrough, preferably circular, to receive one of the ultraviolet lamp ends. The second support includes a noncircular constraint that is secured to the other of the opposing ultraviolet lamp ends. A saddle or yoke is secured relative to the tunnel at approximately the same height as the first ultraviolet lamp support. This saddle receives the noncircular constraint in either of two oppositely oriented dispositions. This allows the ultraviolet lamp to be oriented horizontally alternatively to face in either of two opposite directions.
Preferably the noncircular constraint is an oblong block which may have a rectangular configuration. The saddle then defines an upwardly facing channel having vertical sides and a horizontal bottom and is configured to receive and snugly seat the rectangular constraint therewithin. The opening through the first of the ultraviolet lamp supports is large enough to permit the elongated lamp to be tilted relative to the first of the ultraviolet lamp supports.